1. Field of the Invention
This invention relates to a method of manufacture for extruded trim strip used for the sides of automobiles and for other purposes.
2. Acknowledgement of Prior Art
Trim strip on the side of motor vehicles has been traditionally added both for decorative purposes and to act as protection for the body work. The strips may be used for body side mouldings for front and rear quarter panels and side doors. They must meet exceptionally high standards for colour uniformity and match. Moreover, they must have distinctive end shapes to meet manufacturing requirements for customer appreciation.
Such strips have been made by either of injection moulding and extrusion. Both these processes have certain disadvantages. Injection moulding is slow and expensive. It is, however, possible to provide injection moulded strip having shaped moulded ends in a length accurately calculable to that length which is required.
An extruded moulding is much less expensive to produce and may be extruded onto a carrier strip or may be extruded without any carrier strip. When a carrier strip is used it is frequently a strip of aluminum.
Extruded trim strip may be cut to length or may be moulded by various means to produce decorative ends. If the strip is cut to length it will have a cut end exposed throughout the cross section of the moulding. This presents an unattractive, unfinished appearance.
An appreciable amount of effort has been made in the industry to provide extruded trim strip having finished moulded end portions. Methods and apparatus for providing such end portions are described for example in:
U.S. Pat. No. 5,171,499 (Dec. 15, 1992) Cehelnik et al. PA0 U.S. Pat. No. 5,226,998 (Jul. 13, 1993) Few PA0 U.S. Pat. No. 5,227,108 (Jul. 13, 1993) Reid, Jr. et al. PA0 U.S. Pat. No. 5,395,575 (Mar. 7, 1995) Stribbell et al. PA0 U.S. Pat. No. 5,409,653 (Apr. 25, 1995) Malm PA0 U.S. Pat. No. 5,478,516 (Dec. 26, 1995) Malm et al.
The referenced patents are exemplary of the many patents relating to the forming of end portions in extruded trim strip.
While considerable effort and thought has been given to the forming of end portions, a major problem remains. Extruded strip which is not extruded over an integral carrier strip, cannot be produced in lengths which are sufficiently precise for use as automobile trim strip. The reason for this is in the extrusion process itself. When a length of strip is injection moulded, it will shrink on cooling but the shrinkage may be accurately predicted. When extruded strip is formed there is an additional factor in that stresses are exerted in the extruding plastic. As the plastic leaves the die there will be a force from behind pushing it through the die. As the extruded, still softened, plastic moves forward a stretching or pulling force will be exerted on it through its own weight and/or due to the carrier motion of moulding wheels or drums around which it passes to provide pinched or moulded end portions as well as by the take away conveyor which is pulling along through various equipment. This effect will continue until such time that the extrudate has cooled sufficiently to become a solid. The effect on the final length of trim is unpredictable due to the number of variables involved, for example, the type of plastic material, the extrusion temperature, the differing lengths which are required, the adjustment of the speed of the moulding wheels, etc. This problem is so extreme that it may be advantageous to mould or pinch only one end of the trim and provide a partially shaped other end which may be cut, after cooling and/or annealing for final adjustment of the length once the part has stabilized in length.
It is at least partially due to the difficulty in providing accurate lengths of extruded trim strip that integral carrier strips are used but such integral carrier strips also have disadvantages. One obvious disadvantage is that the cost of the trim strip is increased. Another disadvantage is that the carrier strip adds stiffness to the eventual composite strip and there may be a tendency for it to curl outwardly at the ends.
The present inventors have addressed the problems in the art and have attempted to provide an extruded trim strip which does not require an integral carrier strip and which is producible in accurately calculable lengths having moulded ends.